1. Field of the Invention
The invention relates to an injection-moulding device.
2. Description of the Related Art
These injection-moulding devices are also referred to in the art as hot runners, wherein the flow channel for the plastic melt in the device is held at process temperature, whereby the plastic present in the mould can be re-used for a subsequent production cycle. The flow channel is generally embodied in metal and equipped with heating elements and thermocouples, wherein control equipment is present to set a suitable temperature.
A critical component in such injection-moulding devices are the seals. A known seal is formed by a sealing ring which is enclosed with a sufficiently large bias between two parallel surfaces. The ring can be either solid or hollow, wherein the hollow ring has the advantage that liquid plastic will flow into the ring and will contribute toward the sealing action. In such a known seal both the parallel surfaces are at right angles to the channel. The plastic pressure will then press apart both the structural parts of which the sealing surfaces form part. The bias of the ring must therefore be at least as great as the occurring plastic pressure times the projected area of the channel for sealing. This sealing action will be adversely affected by possible movements of the structural parts in axial direction relative to each other.
Such hot runners are moreover subject to considerable pressures of up to 2000 bar and temperatures of about 480xc2x0 C. This makes considerably more difficult the sealing action for transverse separating surfaces in the flow channel. These transverse separating surfaces are for instance present between the manifold and the nozzles connected to the manifold and between parts of the nozzles themselves.
Known from DE 43 24 027 is a sealing ring for bridging transverse separating surfaces between modular components of an injection-moulding device. This known injection-moulding device is applied for the injection moulding of elastomeric objects, wherein wholly different operating conditions occur than in the case of hot runners. The operating temperature is for instance considerably lower.
The invention has for its object to obviate the above stated drawback in hot runners and provides for this purpose an injection-moulding device as according to claim 1. By arranging a sealing element clampingly in the flow channel a sealing is obtained of the surface which is concentric to the flow channel.
The sealing element is preferably provided on the structural components with shrink fit in the diameter and optionally an overmeasure in the dimension in axial direction. In the case of a shrink fit the sealing element is arranged in the flow channel with an overmeasure in the diameter while temperature is decreased, for instance with nitrogen. A relatively large bias can be obtained with shrink fitting. When an overmeasure in the dimension in axial direction is also applied, a sealing action is obtained in the case of two mutually perpendicular surfaces.
Since the seal parallel to the flow channel is more critical than transversely thereof, the sealing element is preferably formed by a cylindrical bush, wherein the ratio of the diameter of the flow channel, wall thickness of the bush and height of the bush equals 22:2:10. The plastic pressure will press the thin-walled bush against the wall of the flow channel. The higher the plastic pressure, the better the sealing action will be. Should both structural components move axially or rotate relative to each other, the sealing capacity will not then be affected, or only slightly.